ABSTRACT This F31 project aims to advance understanding of the manifestation and trajectory of maternal depression among adolescent women (age 15-19) compared to adults throughout pregnancy and postpartum, and to develop a risk score to identify pregnancies at high risk for adverse perinatal outcomes. Approximately 13% of peripartum women worldwide report mental health issues, predominantly depression. Adolescence is a period of substantial developmental and hormonal changes which add to physiologic and psychosocial changes in pregnancy. Frequency of depression among adolescent pregnant and postpartum women is up to 30% higher than their adult and non-pregnant counterparts. Perinatal depression among adolescents has not been rigorously characterized in a large-scale, longitudinal study. Almost all adolescent pregnancies (95%) worldwide occur in low- and middle-income countries (LMICs), yet few data exist on maternal depression among adolescents in these settings. A recent systematic review found higher prevalence of maternal depression in LMICs (16% in pregnancy, 20% in postpartum) than in high-income country settings (HICs). Several studies in HICs have linked depression and adolescence to preterm birth and low birthweight, yet critical gaps remain in understanding implications of maternal depression on perinatal outcomes within SSA where the burden of infant morbidity and mortality is highest worldwide. The proposed F31 research project leverages data collected in an ongoing randomized cluster trial (PrIMA Study, R01AI125498, MPI: John-Stewart/Baeten) among adolescent and adult pregnant Kenyan women (?15 years old) who are followed through 9-months postpartum. We are screening >4000 Kenyan women (median age: 24 years, ~25% age <20 years) longitudinally via antenatal/postnatal care (ANC/PNC) for depressive symptoms. In Aim 1, we will use data from initial ANC, 6 weeks PNC, and 9 months PNC to longitudinally compare maternal depression among adolescent versus adult women, identifying predictors, symptoms, and changes in prevalence and severity to inform future interventions. In Aim 2 we will develop and validate an empiric risk score to predict adverse perinatal outcomes that incorporates depressive score in pregnancy and other maternal factors (e.g., adolescent age). Results from Aim 2 will contribute a clinical prediction tool to inform who may need intensified monitoring to avert adverse perinatal outcomes like preterm birth and low birthweight. This large-scale study to longitudinally compare depression among adolescents and adults from pregnancy through 9 months postpartum will contribute a novel clinical prediction tool using depression score to predict perinatal outcomes. This research plan will provide the F31 candidate rigorous predoctoral training including 1) quantitative analysis of longitudinal data, 2) experience developing and internally validating a risk score, and 3) content-area expertise in maternal depression, an area critical to closing gaps in maternal, adolescent, and child health.